[s0ulphire]

Yes exactly right, which is what the Israeli data has indicated. It's not a huge decrease, but there's a definitive slow decrease in efficacy - worth noting it's nearly entirely against the Delta variant again though. So even though 2 shots will continue to keep you moderately safe, the argument is that there's no good reason to not get a booster (just like a flu shot every year).

edit: to quote specifics from the study

> Our findings are in line with findings from the randomized trial of the BNT162b2 vaccine, which showed a reduction in vaccine efficacy against symptomatic infection from 96% in the first 2 months after vaccination to 84% at 4 to 7 months after vaccination, when averaged over all age groups combined